Method and apparatus for heat transmission



July 23, 1935.

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I METHOD AND APPARATUS FOR HEAT TRANSMISSION '4 Sheets-Sheet 3 Filed April 2, 1934 INVENTOR P I BM 5% Me /5n,

. 3 m/zafimnf m ATTORNEYS H. E. A. GUTH 4 Sheets-Sheet 4 Wf/M ATTORNEYS July 23, 1935.

METHOD AND APPARATUS FOR HEAT TRANSMISSION Filed April 2, 1934 Patented July 23, 1935 PATENT OFElCE DIETHOD AND APPARATUS FOR HEAT TRANSMISSION Hans Elis Abraham Giith, Stockholm, Sweden,

asslgnor to Stockholm, Sweden, company Induatrikemiska Aktiebolaget,

a Swedish joint-stock Application April 2, 1934, Serial No. 718,737 In Sweden May 22, 1930 a 22 Claims. ((1159-16) This invention relates to methods and apparatus for the transmission of heat, and more particularly to methods and apparatus of this character that involve the evaporation of liquids.

It is.known that evaporation can be efiected at atmospheric pressure by circulating the liquid to be evaporated alternately through an apparatus wherein it is heated by indirect contact with a condensible medium and through an apparatus whereinit is cooled by direct contact with a permanent gas or a vapor mixture containing a permanent gas. It has also been found that the gas vapor mixture obtained as a result of the cooling or evaporating step may be used as the condensible heating medium in the heating step of another phase of a multiple effect process, and that-the relatively dry gas which results from the indirect heating step of any particular phase may likewise be utilized as the cooling or vapor absorbing medium in the evaporating step of some 7 other phase.

For example, the application for United States Letters Patent of Erik Oman, Serial No. 362,976, filed May 14, 1929, discloses a simplified multiple eflfect evaporating process wherein the whole apparatus is rendered operable under one and the same total pressure, such as atmospheric pressure, by the use of a permanent gas, or. gases, in mixture with vapors in giving ofi heat to-a liquid and in evaporating the same. Furthermore, my

own prior application, Serial No. 513,240, filed" 'February 4, 1931, discloses how, in order to obtain high efllciency from the standpoint of heat economy, such an evaporating process should preferably be divided into two stages: first, the

heating of the liquid to be evaporated, and, sec,- ond, the cooling of the same by evaporation, both of these heat exchanging operations preferably taking place during a counterflow of the respec- 9- tive bodies of liquid and gas or gas vapor mixture between which the exchange of heat takes place.

As is disclosed in the last mentioned applica-.

.tion, it may be stated, as a general rule, that 43 in the heating of the liquid by indirect contact with a condensing gas vapor mixture it is ime portant that the mixture be cooled down to as low a temperature as possible, a result which is attained by =maintaining the initial. temperature 5: of the liquid also as low as possible. At the same time, itis also important, particularly where multiple efiect evaporation is the object, that the sat-.

uration temperature of the newgas vapor mixture which is obtained at the subsequent evaporation 1 5 of the-heated liquid should be as high as possible.

Whenthe liquid is circulating, and is alternately cooled by evaporation and heated by indirect heating, the initial temperature of the liquid at the beginning of the indirect heat exchange-will depend ,ultimately upon how far the 5 cooling by evaporation is carried. Consequently, the heat economy of the whole method will be dependent upon the manner in which the evaporation is eflected. Since the amount of vapor which can be taken up by a cooling medium con 1 taining a certain amount of a permanent gas, such as air, before saturation depends upon the temperature prevailing during the evaporation (increasing where the temperature is rising), and since the prevailing temperature is greatest at the 15 point of entrance of the hot liquid into an evapcrating apparatus, the evaporative process would be substantially improved in efllciency if the difference between the temperature of the liquid and the saturation temperature of the gas were to be increased where cold gas ,is entering the liquid cooling or evaporating step, and, on" the other hand, decreased where hot-liquid is entering the same step.

The present invention relates to a novel method and apparatus for carrying out such an improved evaporating process. However, before proceeding with a detailed description of the method and apparatus forming the subject matter of ,the invention, it is deemed advisable to first explain the ,4 theoretical aspects of the process of evaporation of a liquid by direct contact with a permanent gas which preferably flows in countercurrent to the liquid, reference being had for this purpose to Figs. 1-4 of the accompanying-drawings wherein are graphically illustrated the phenomena in question.

In connection with this explanation, it is assumed that the liquid to be evaporated consists of water and that the permanent gas is air, algo though it will be understood that the fundamental principles are the same for other liquids and gases. It is also assumed that a certain quantity of water of a constant initial temperature is passed in direct contact with and in countercuri rent to a certain quantity of air also of constant initial temperature, whereupon evaporation takes place, the water is cooled and the air is saturated to a higher temperature. 'Ihe cone tact surface between the air and water is assumed go to be infinite in extent. All temperatures are expressed in degrees centigrade.

The calculations involved are based upon'known tabular values of the content of water vapor in saturated airat a total pressure of'760 mm. of

30 sented by such a'line is relatively simple.

mercury and at diiferent temperatures, and upon curve shown therein indicates the total heat (calculated from.0-C.) of 1 kilogram of air saturated with steam at temperatures between 15 30 and 75, the temperature oithe air vapor mixture being plotted on the abscissa in degrees centigrade, the heat content of the mixture being plotted on the ordinate in kilogram calories. It will be recognized that the curvature of the line 15 of Fig. l is'due to the similar shape of the steam pressure curve. if the process of cooling or heating a certain quantity of liquid should be reproduced in a diagram of .this character, such a process would 20 berepresented by. a straight line (the inconsequentialchanges in the specific heat of the liquid being disregarded). For example, in the diagram shown in Fig. 2, line (1 represents the process of cooling 1 kilogram of water from 70 to 25 30, or heating the same from 30 to 70, while line 1) indicates a' similar cooling or heating of 2 kilograms of water between the temperatures of or and 20.

The calculation of the quantity of liquid repre- Line hgives, for instance:

Fall of temperature: 40-20=20 Quantity of heat given off (or absorbed) =40 v I 35 I Specific heat of water=1.

Quantity of liquid=g%=2 kilograms IflinebinFlg.2isshiftedparalleltoitself so in the vertical direction, the new line 1; thus 7 obtained indicates only the rate of variation in the heat content of the liquid in heating or cooling, and differs from the line b in that the end points thereof no longer indicate the total'heat 45 content of that particular quantity. oif liquid at the respective temperatures.- In other words, in

a diagram such as Fig. 2, the line b or b represents a quantity of liquid wherein the heat content varies according to the heat variation of 5 the quantity represented by line arhowever, as

- lifieb" does not pass through the same zero point as do lines a and b, the total heat content of the quantity of liquid represented by b at any par--v ticular temperature cannot'be determined by a 55 simple observation of the ordinate of a point on that line corresponding to the temperature in question.

Actually, lines a and I). under these conditions represent the'heat exchange which would take 60 place between the two liquid quantities referred to in the diagram when flowing in indirect coni a tact with and countercurrent to one another.

In other words, Fig. 2 is a graphical illustration of the exchange of heat which takes place .when 1 kilogram of water is cooled from 70 to 30 by,

'65. indirect heat exchange with 2 kilograms of water the temperature of which is thereby raised from- A 20 to40.

. Now let it be assumed that the initial temper- 70 ature of the water is 65, that the initial temperature of the saturated air is,l?, and-that the water is to be cooled by evaporation to 3 0". Un der these conditionathe pr lem is to ascertain whether it wouldbe possible to obtain a final 75 samration temperature of theair of 64, for ex- Fig. 1 shows that the total heats of saturated air at 64 and 15 are 137and cal./kg., respectively: Accordingly, in order to raise the temperature of 1 kilogram of saturated air from l5" to 64 by heat exchange with water, the wa- 5 ter would be required to give 011 1:37-10:12? calories during the process. The initial and final temperatures of the liquid having been fixed at 65 and 30"., the quantity of liquid required for the process would be ,f=3.65 kilograms. I

Under these conditions, the process of the evaporation would be represented by the curve A.-lB and the line D-.-E in the diagram shown in Fig. 3' of the drawings. The line D-E is obtained by shifting a line corresponding to the above mentioned quantity of liquid between the temperatures of 30" and 65 parallel to itself, as

Y discussed above in connection with Fig, 2, until point E coincides with the point havingthe coordinates t==, cal.=l0, corresponding to the ,.,initial condition of the air, t=15, cal.=10.

It will be seen that line 13-11 intersects the curve at two points, 0 and d. If the process of evaporation were really that indicated in the diagram, then, during that portion of the process which takes place between the points 0 and (1, heat would be transmitted from a colder to a warmer medium, an obviously impossible condition. Therefore, if transmission of heat from the water to the air vapor mixture is to be actually possible, the straight line representing the cooling of the liquid must obviously, never intersect the curve A--B, but must pass to the right thereof, or at the most be tangent thereto.

Thus it follows that is'is not possible in a process of this kind, where the initial and flrial temperatures of the water and the initial tem- 40 peratureof the air are fixed, to choose arbitrarily the final temperatureof the saturated air; but the latter is limited to a certain temperature, less than the highest temperature of the liquid,

which is determined by the temperature drop which the liquid is to undergo during the evaporation (in the above example, cooling from 65 If, in Fig. 3, a straight line is drawn from the point E tangent)! curve A--B, as ate, said line will intersect a vertical line corresponding to t= at D. A horizontal line drawn through D will then intersect curve A--B at C, a point corresponding to t=59. Point C (59) therefore. represents the highest saturation temperature to 5 which 1 kilogram of. air can be raised during the evaporative cooling from 65 to 30 of the quantity of water represented by line D'-E, assuming an infinite contacting surface between the air and liquid. 6 Since the line DE, by reason of its smaller inclination, represents a smaller quantity of liquid than the line 13-11, it is obvious that with the larger quantity of liquid represented by D-E a larger quantity of air than-1 kilogram could be saturated to-5,9. I While in the above example it is not possible to reach a saturation temperature higher than 59, it is evident that under other conditions it woukLbe possible to obtain a higher saturation ,6

' temperature. For example, this'may be effected by maintaining the final temperature of the' liquid higher; that is, by using a/comparatively smaller quantity oi!v air for the evaporation.

[Such a process isillustrated by the following example. I

' corresponding temperatures which are attainable- Assumingthat a final saturation temperature of64 is desired, and that the initial temperature of the air is then 127 calories" must be exchanged per kilogram of air,.v as above indicated.- The problem is then, to determine how far the liquid can becooled.

Referring to the diagram shown in Fig. 4, the curve A--B represents the process of raising the temperature of saturated air from 15 to 64. A horizontal line passing through pointB intersects a vertical line corresponding to t=65 at D. If a line is then drawn tangent to curve AB, it will intersect a horizontal line through point A at E, corresponding to t:41.5. The slope of line DE' indicates "the quantity of liquid that would be required for the process, and the point E indicates that the lowest attainable exit temperature of the liquid will be 415.

When the liquid is to be circulated in the evaporating apparatus-that is,,to be cooled by evaporation in one step and. then heated in a subsequent step preparatory to a second evaporation-this higher exit temperature after cooling or evaporation naturally results in an initial tion of the heat content of said mixture.

'character of the steam pressure curve. As the steam pressure curves of all liquids are of similar form, the same conditions will always prevail, no

, matter what liquid and what gases are under consideration.

In view of the facts and phenomena set forth above, it should be clear that, in the evaporation of a fixed quantity of a liquid by-mea'ns of another fixed quantity of a gas in direct contact therewith and flowing in countercurrent thereto, it will not be possible, if the initial temperatures of the liquid and the gas are fixed, to arbitrarily vary.both exit temperatures.

inherent limiting value for the other beyond whichit is physically impossible to go with the character of process thus far disclosed. It should be obvious from the above values of attainable temperatures, however, that, even if itis not possible to reach the extreme limits of cooling and heating which at first seem possible, it is nevertheless possible to effectually utilize the source of heat and simultaneously obtain a useful air vapor mixture. Thus it is always possible on this basis to construct a multiple effect system.

However, the difliculties of effectively lowering the temperature of the liquid in the evaporation process, without at the sameltime lowering the exit saturation temperature of the air vapor mixture too much below the initial temperature of the liquid, become greater the higher the temperature of the entering liquid.

It is therefore the principal object of the present invention to overcome these difliculties which are inherent in evaporation processes utilizing fixed quantities of liquid and, gas, and to pro vide both a method and apparatus tor carrying out the evaporative process wherein the exit temperature of the liquid and the. exit saturation temperature of the gas vapor mixture are materially lower, and higher, respectively, than the If one of the exit temperatures is fixed, there will be an in processes hitherto known to the art, thereby substantially improving their over-all efliciency. More broadly, it isthe object of this invention'to provide a novel method and apparatus for the transmission of heat between a liquid and a gas or a gas vapor mixture wherein the ratio of the quantity of liquid to the quantity of gas or gas vapor mixture is varied during the heat transstages during the evaporative heat. exchange,

and may be eifected either by a reduction in the quantity of liquid with respect to a fixed quantity of gas or gas vapor mixture, or by a reduction in the quantity of the gas or gas vapor mixture with respect to a fixed quantity of liquid, or by a combination of both of these procedures.

The variation may also be accomplished by using separate, different quantities of either liquid or gas vapor mixture in successive stages of the process, or each stage may have its own individual quantities of both liquid and gas vapor'mix ture.

If the variation in ratio is efiected by with- 7 drawing some of the liquid and thereby reducing its quantity as compared with the quantity of withdrawn, the heating of both quantities thereaf er continuing together.

The invention will be more clearly understood by reference to the accompanying drawings wherein several diiferent embodiments of the method and apparatus constituting the present invention are disclosed, it being distinctly understood, however, that these drawings are for the purpose of illustration only and are not to be construed as defining the scope of the invention, reference for the latter purpose being had to the appended claims.

In the drawings, wherein like reference characters indicate like parts throughout the several views:

1 Figs. 5, 6 and '7 are diagrams, somewhat similar to Figs. 3 and 4, graphically illustrating three different embodiments of the methodof the present invention as appliedto the evaporation of a liquid by direct'contact with and in counterflow to a gasor a gas vapor mixture;

Fig. 8 is a schematic diagram'of one form of apparatus embodying the present invention wherein separate, diflerent quantities of liquid are successively indirectly heated and cooled by evaporation by the same quantities of heating medium andgas or gas vapor mixture, respectively;

Fig. 9 is a diagram similar to Fig. 8 of another form ofapparatus embodying the present in- V temperatures.

' supplied to the first stage is perature of 64,

variation in the quantity of the liquid between said stages;

Fig. 10 is a. diagram similar to Fig. 8 of still another form of apparatus embodying the present invention wherein the variations in the ratios above mentioned are efiected by adding to or withdrawing from the quantity of gas or gas vapor mixture which is being used for heating or evaporating a fixed quantity of liquid; and

Fig. 11 is a diagram ofan apparatus embodying the ieatures of both Figs. 9 and 10.

Referring first to Fig. 5,- there is indicated therein a two-stage evaporative process whereby water may be cooled from 65 to 30 by direct perature of 15 and a flnal saturation temperature of 64, the conditions which it was found could not be met in a single step process such as that indicated in Fig. 3. As shown, in'the first stage of the process a certain quantity of air havingan initial saturation temperature 01 15 is flowed in direct contact with and countercurrent to a quantity of water having an initial temperature of 52. During the counterflow evaporation takes place which lowers the temperature of the liquid to 30 and at the same time raises the saturation temperature of the air to 48. The air is then brought into contact with and continues its flow counter to that of another and larger quantity of liquid, evaporation oi which raises the saturation'temperature of the air to 64 while the liquid is cooled from 65 to 52.

In the first stage, the heat content of the liquid is reduced by 60-19=50 calories while the temperature of the liquid is lowered 52-30=22. Hence the calculated quantity of liquid which is 2.28 kilograms Computed .in the same manner, the quantity of liquid which can be cooled by evaporation in the second stage of the process is 5.77 kilograms Since it is assumed that the amount or heat given off by the liquid is absorbed without loss by the air during the evaporating process, the total heat content of the air. during its heating from 15 to 64 increases from 10 to 125 kg. cal. Since, according to Fig. 1, 1 kilogram of dry air takes up approximately -10=130 kg. cal. in being heated from 15 to 64, a gas vapor mixture containing 12.=. v i- 0.96 kilogram of dry air is necessary for cooling the above quantities of liquid by evaporation between the stated Carrying out the evaporation in this mannerinvolves a decided advantage over and results in a greater efliciency than the single step evaporative processes hitherto known. It will be seen from the diagram and. the above numericalexcontact with air having an initial saturation temample that the air vapor mixture obtained in the evaporating process has an exit saturationltemand also that a portion of the liquid can be cooled down to an exit temperature of 30. Thus, bydrawing ofi a portion of the liquid after it has been cooled from its initial temperature by a certain amount, and then continu ing the cooling evaporative process with the reduced amount of liquid but with the same amount of air--that is, by reducing the ratio of the quantity of liquid to the quantity of the air vapor mix-5 ture during the course of evaporation--it is possible to accomplish results which are shown in Fig.3 to be impossible of achievement with fixed quantities of both liquid and air. The quantity of liquid cooled to 30 9.156 makes possible a more effective utilizationoi the source of heat in the subsequent repeated heating of the liquid in processes where alternate heating and cooling are employed and where the heating medium comprises a condensible gas vapor mixture.

In Fig. 6 there is diagrammatically illustrated an evaporating process wherein the same initial and exit temperatures of both liquid and gas are obtained as in the process of Fig. 5, but wherein the variation in the ratio between the quantities of liquid and gas or gas vapor mixture is attained by decreasing the quantity of the gas by withdrawing a portion thereof at a point intermediate the beginning and ending of the evaporative process while maintaining the quantity of liquid constant. It will also be noted that the total heat transferred during the process of Fig. 6 is less than in the process of Fig. 5.

As shown, a certain quantity of air having an initial saturationtemperature of 15 is flowed in direct contact with and countercurrent to a quantity of the water to be evaporated until the sa ration temperature of the air is raised to 48. At the same time, the liquid is cooled from a temperature of 52 to 30. At this point, some of the air vapor mixture is withdrawn and the evaporative process continues with the smaller quantity thereof in contact with the same quantity of liquid that was used in the first mentioned stageof the process. This second stage raises the saturathe quantity of liquid remains the same as in the first stage (2.28 kilograms) but the iguantity of dry air contained in the air vapor mixture is substantially reduced. In. this second stage, the saturation temperature of the air vapor mixture is raised from 48 to 64, during which increasein temperature the total heat content of 1 kilogram of dry air, as computed from Fig. 1, would increase 13760=77 kg. cal. However, at the same time, the water gives up 90-60:30 calories, all of which it is assumed is absorbed by the air with which it is in contact. Consequently, a gas vapor mixture containing I 0.39 kilogram pfdry air is necessary for cooling the 2.28 kilograms of liquid from 65 to 52 dm'ing the second stage 0! the evaporative process. The process illustrated by the diagram of Fig. '7 is a combination of the processes of Figs. 5 and 6 in that the variation in the ratio between the quantities of gas or gas vapor mixture and liquid is accomplished by varying both the quantity of gas and the quantity of liquid in the two stages 01' the process; In this instance, it will be noted b1 the liquid from 65 to 30" is intermediate 3 the quantities transferred in the processes o! Figs. 5 and 6. By computations similar and 6, it can readily be established that by uitilizing a'gas vapor mixture containing 0.96 'kilogram' from 48 to 64, 4.23 kilograms of water can be cooled by evaporation ,from 65 to 52, and 2.28 kilograms thereof then cooled from 52 to 30, thereby again attainingthe advantages and im proved results discussed above in connection with the process illustrated in Fig. 5. 7

Having now described in detail the concept of the present invention as applied to the process of evaporation, reference may, now be had to Figs. 8-11 wherein there are disclosed various forms of apparatus'by which the method of the present invention may be practiced. In general, such an apparatus comprises a suitable arrangement of means for fiowinga liquid and a gas or gas vapor mixture in direct contactwith but coimtercurrent to one another during which fiow heat may be transmitted between the gas,

or gas vapor mixture and the liquid, as by evaporation of the latter, and means for varying the ratio between the quantities of gas or gas vapor mixture and liquid during the heat transmission by either drawing ofi a portion of the liquid or withdrawing a portion of the gas or gas vapor mixture at some point intermediate the beginning and ending pf the heat transmission process. It is also preferable that the means for carrying out the heat transmission or evaporation be combined with a suitable heater or heaters wherein the liquid may be heated, preferably by indirect contact with a' condensible gas vapor mixture; prior to entering the evaporating apparatus.

Referring first to Fig. 8, there is die an o tically illustrated therein an evaporating" system operating upon the principles above set forth, and corresponding to the evaporating process indicated in the diagiamotFig. 5. In the-embodiment disclosed, the variation in the ratio between the quantities of gas orv gas vapor mixture and liquid is attained by. utilizing entirely separate, diiferent quantities or liquid in the two stages of the evaporative process while at the same time maintaining the quantity of gas or gas vapor mixture constant in both of said stages. Furthermore, the heating of the liquid prior to evaporation is also divided into two stages in both of which the same quantity of heating medium is utilized with the difierent quantities of liquid, thereby increasing the efliciency oi the heat transfer in the same manner as has previously been described in connection with the evaporating process.

As shown, the heating takes place in a pair of heaters 92 and it of any suitable character, while the evaporation is eflected in'evaporato'rs Ed and 95. Preferably, each of the heaters comprises an outer chamber it tor the heating vmedium and an inner separate chamber it through which hows the liquid to be heatedthe heat transmission taking place through the relatively thin walls of inner chambers it. Each of the .evaporators, however, consists of a single ir wherein the liquid and gas or g' vapormixture are in direct contact with but flow in P1.

. that the total heat transferred during the coolto those above set forth in connection with the'processes Figs.

tercurrent to one another. Heater l2 and evaporator N form one system while heater I3 and evaporator form another, and the two systems are so designed as to operate with difl'erent quantities' of liquid.

Heaters l2 and I! are provided with conduits l8 and I9, respectively, which supply difierent quantities of liquid to the tops of inner chambers l1 and direct the liquid against the walls thereof in such a manner that it flows downwardly thereover in relatively thin layers. bottoms of inner chambers H the" two difierent quantities of now heated liquid are conducted by conduits and 2|, respectively, to the tops of the chambers of evaporators l4 and I5 where the liquid is again directed against the walls of V 29, respectively, .controlled by valves and at,

into suitable collecting vessels 82 and 33.

Heater i2 is also provided with a conduit 34 connected to the bottom thereof and leading into the outer chamber 86 through which a condensible gas vapor mixture may be supplied for heating purposes. The heating medium supplied through conduit 34 flows upwardly through outer chamber it, giving up its heat to the counterflowing liquid in chamber H, and passes from the top of heater 82 through a conduit 85 to the bottom of heater 83 at which point it enters outer chamber l6 thereof. After flowing upwardly through heater M, the heating medium is drawn 03 from the top thereof through the conduit 36 whence it may be supplied to the evaporating apparatus of another unit or otherwise disposed of in any suitable manner.

The flow of the evaporating gas or gas vapor mixture is opposite to that of the heating medium in that it is first supplied to evaporator l5 where it comes into contact with the liquid from heater is, the latter constituting the second stage of the heating process. As shown, the evaporating gas or gas vaponmixture is supplied to the bottom of evaporator i5 through a suitable conduit 3?, flows upwardly through the chamber of said evaporator in direct contact with but counter-current to the liquid therein, is conducted from the top of evaporator i5 through a conduit 38 to the bottom of evaporator it, and after upward flow therethrough is drawn off from the top thereof through conduit 39. The gas vapor mixture leaving evaporator it through conduit 39 is supplied to the heater of another unit and there utilized asithe heating medium.

In operation, the liquid is supplied to the system comprising heater l2 and evaporator H in a relatively larger quantity thanit is to the system comprising heater is and evaporator 05. As indicated byway of example in Fig. 8, the temperature of the liquid supplied to heater t2 may be approximately 52, and in its downward passage therethrough may be heated to approxi- 10 From the e orator I4 wherein it may be cooled by evaporation to 52 by agas or gas vapor mixture having an initial saturation temperature oi .48 and an exit temperature of 64. On the other hand, the liquid supplied to heater I: may have an initial temperature of 30 and be heated to 52 by the heating medium leaving heater 1!, the temperature of which will be 64 at entrance and 40 'at exit. This relatively smaller quantity of liquid leaving heater II at 52 may then be cooled by evaporation back to 30 in evaporator 15 by the same quantity of gas or gas vapor mixture which passes through evaporator H, but during the time that the temperature thereof is first raised from 15 to 48.

lit will be obvious from a comparison of the temperatures ofthe various quantities of liquid and gas or gas vapor mixture above-referred to that the apparatus thus described is capable of carrying out the process indicated in Fig. 5. I

Suitable means, such as a cross connecting conduit 4| indicated in dotted lines in Fig. 8, may also be provided for transferring liquid from the system comprising heater l2 and evaporator N to the system comprising heater i3 and evaporator ii, and vice versa, for the p'urpose of regulating the ratio between the different quantities of liquid in the two systems, or for regulating the concentrations thereof. It will be noted that the transfer oi! liquid through conduit preierablytakes place, between points where the liquid in "the two systems is of thesame tem- 'perature.

As pointed out above, heater f2 and evaporator II, and heateril and evaporator l5, form two. separate systems with respect to the circulating quantities'oi liquid. Theonly condition other than those specified that must be met in order for the evaporating process to take place in accordance with the diagram of Fig. 5 is that the quantities. or liquid circulating-in .the two systems conform to theratio 2.28:5.77. In Fig. 9 there is shown an evaporating system in which the temperatures are the; same as in theap'paratus of Fig. 8, but in which the variation. in the ratio between the quantities of liquid and gas or gas vapor mixture is effected by drawing oi! a portion of the liquid during the, evaporative process. y

In the apparatus shown, l2- and-l3 indicate-the heaters, and I4 and IS the evaporator-s, as in the embodiment of FlgsS. However, it will be noted that, as a matter 01 expediency, the two heaters may be combined in a single, outer casing so that the two outer chambers I are continuous one with the other. The heating medium enters the bottom the combined heating unit through a conduit ll at a temperature of 75, and leaves through a conduit 42' at a temperature M40". The liquid, which enters ough conduit l3 and leaves through conduit I, is raised in temperature from 30 to 65 by heat transmitted from the heating medium. The liquid thus heated is then supplied bya pump 45 through a conduit ltjto the evaporator 14. After passingv through thisevaporato the liquid is divided into two. parts, one of which passes through the, conduit l1 the evaporator l8, while the er dug]! the cm connecting cond t 40 to the'heateru. M

"Air cl a saturation" temperature of 15 is introduced'hrthe bottom of evaporator I! through the conduit 49, passes through the evaporator I! in ecunterflow to the liquid and is heated to a saturation temperature of 48, then through tile L.

conduit 50 to theevaporator M, and leavesthe latter at at a saturation temperature of 64. That portion of the liquid which passes through evaporator l5 leaves through the conduit-52' and is supplied by means of a pump 53 through a conduit 54 to the top of heater l3. Fresh liquid may r.

be supplied through conduit 55, when desired, while concentrated liquid may be drawn of! at 56.

The temperatures shown in Fig. 9 correspond to a branching of! of a quantity of liquid through the conduit 40 equal to of the liquid quantity leaving the evaporator 14.

,As previously stated, the variation in the ratio between the quantities of liquid and gas or gas vapor mixture may also be varied by decreasing the quantity oi gas utilized in successive stages of the process while maintaining the quantity of liquid constant, or by varying the quantities of both liquid and gas. In principle, these procedures do not differ from those above described, inasmuch as the improved results which flow from the present invention are obtained because of the variation inthe ratio between the gas and liquid quantities, irrespective of the specific man: her in which that variation is effected.

For example, the method 'of the present invention'may also be carried out in apparatus such as that disclosed in Fig. 10, wherein the variation in the ratio referred to is eifected by vary-,

'ingthe quantity of gas or gas vapor mixture which is utilized during different stages of the process, according to the process illustrated by the diagram of Fig. 6.

\As shown, the apparatus comprises a heater 51 a relatively long casing in which are provided. an outer chamber 58 and an inner chamber 50, corresponding to the chambers i6 and ll of Figs. 8 .and 9, and an evaporator 60. A certain quantity. of the heating medium at a temperature of 75 is supplied to the bottom of heater 51 through a conduit 6|, while an additional quantity at a lower temperature of -64", for example, 'is supplied through conduit 62 at a point intermediate the ends 01 the heater. All of the heating medium is-withdrawn from heater 51 at the top thereof through conduit 63, at which point it has all been cooled to a temperature of $02 The liquid to be heated is supplied to heater 51 at the top 0! 'chamber 59 through a conduit 64 at a temperature of 30 and leaves through conduit I 'at a temperature of 65" whence it is supplied by means of a pump 66 through a conduit 81 to the top of evaporator 60. In passing. downwardly through evaporator 60 in direct contact with and countercurrent to the cooling gas-or gas vapor mixture, the liquid is cooled from 65 to 30, and after leaving evaporator 60 isreturned to the top of heater 5! by means of a pump 68 and through a conduit 69. The cooling gas or gas vapor mixture is supplied to the bottom of evaporator 60 through conduit II at a temperature of 15 and passes upwardly in heat exchange contact with .and

-coimtercurrcnt to the liquid until its saturation temperature has been raised to 48 at which time a portion of the gas is drawn oil through conduit ll, The remainderot the "gas continues its flow through the evaporator to the top thereof. at which point' it is drawn oi! through conduit list a temperature of 64. I v

'The temperatures thus indicated correspond ture leaving evaporator 60 through conduits H and M have been heated and saturated with steam by contact with the liquid, they are capable of use for indirect heating of liquid in the heater of another system of the same type.

,In such event, as is indicated in Fig. 1.0, the gas vapor mixture leaving, evaporator 58 through conduit l2 will enter the heater 53 of the following system at the bottom thereof, while the quantity of said mixture which is drawn' oil? through conduit ill will be introduced at some suitable intermediate point. Similarly, the heating medium leaving heater 5? through conduit $3 at 40 may, if desired, be returned to the evaporator of the preceding system and introduced thereinto as the evaporating medium through a conduit corresponding to conduit it.

The apparatus shown in Fig. 11 combinesthe features of both Figs. 9 and 10, and provides a system wherein the variation in the ratio of the quantities of liquid and gas or gas vapor mixture is efi'ected by changing the quantities of both the liquid and the gas or gas vapor mixture. As

shown/the heater N of the first system or unit is similar to that shown in Fig. 9 in that it has two separate liquid chambers it within a common casing which forms one elongated gas cham-' her it. The liquid to be heated is supplied to heater i l through a conduit 43 at a temperature of 30, and after passing through both sections of the heater is withdrawn through conduit M at a temperature of 65. Theheatingmedium, however, is supplied to heater it in two portions, as in Fig. l0,one portion entering the bottom of the heater through conduit ti at a temperature of 75 and another portion entering through conduit 62 at64 at the point where the liquid passes irom the upper to the lower inner chamber ill and is increased in quantity by the portion which is withdrawn from the evaporator M through conduit All of the heating medium leaves heater M through conduit 63 at a temperature of 40. The heated. liquid leaving the heater through conduit M is supplied by pump 35 through conduit 68 to the top of evaporator it. After passing through evaporator it, a portion of the liquid is drawn ofi through conduit 48, as previously mentioned, the remainder continuing the evaporative process in evaporator iband finally being drawn oil through conduit 52 and recirculated by pump 53 through conduit 56 to the top of heater id.

While the treatment of the liquid in the evaporating process is similar to that-shown in Fig. '9, the apparatus of Fig. 11 also includes means for varying the quantity of the evaporating gas or gas 'vapor mixture in the manner indicated in Fig. 1!).

Accordingly, gas or gas vapor mixture at a temperature of 15 is supplied .to the bottom of evaporator 15 through a conduit l0, and, after passing upwardly through evaporator and having its temperature raised to 48, a portion thereof is withdrawn through conduitill and supplied to an intermediate point in the heater 15 of the next succeeding unit'or system. The remainder of the evaporating gas or gas vapor mixture passes upwardly through conduit 50 and evaporator it to exit conduit "I2 whence, at

In order to carry out the process indicated in the diagram of Fig. 7 by means oi the apparatus 4 shown in Fig. 11, it is necessary that the quantity I a temperature of 5 64", it may be supplied to the bottom of heater "16, as in Fig. 10. 7

obthe' total liquid quantity leaving evaporator i4, and that: the quantity of .gas withdrawn through conduit H be equal to .96 oi the total gas quantity leaving the top of evaporator ib.

Obviously, the above described methods and apparatus for efiecting evaporation are applicable no matter what liquids or liquid'mixtures or gases or gas mixtures are involved. 7

It will be understood that in actual practice the processes above described will be somewhat more complicated in so far as the computation of the exact temperatures and quantities is concerned-because of the fact that the respective quantities of liquid are not actually constant throughout the evaporating process due to the evaporation itself. However, the small discrepancies which would therefore exist betweenthe values shown in the drawings and above referred to and the actual values are immaterial for an understanding of the principle upon which the present invention is based and .in no way afiect the inventive concept.

Itwill be evident that the invention is not limited to processes of two stages but that the, evaporating process may be subdivided into any suitable number of stages or intervals, each operating with a suitablequantity of liquid in the manner above described. Likewise, a plurality of systerns or units may obviously becombined with ried into effect. It will also be apparent that the ple. Likewise any suitable gas or gas vapor mixture may be utilized in place of air as disclosed. Various other changes, which will now appear to those skilled in the art, maybe made in the details of construction and arrangement of the parts of the apparatus, and in the various steps of the process, without departing from the spirit 'of the invention. Reference is therefore to be had to the appended claims for a definition of the limits oi the invention.

This application is a continuation in part of myapplication Serial No. 538,931, filed May 21'. 1931.

What is claimed is:

[1. In a method of transmitting heat between a liquid and a gas-or gas vapor mixture, the steps comprising flowing the liquid and gas or gas vapor mixture in heat exchanging relation with but countercurrent to one another; and increasing the ratio of the quantity of liquid to the quantity of gas or gas vapor mixture when the temperatures thereof reach predetermined points intermediate the desired initial and final temperatures.

2. In a process of evaporating liquids which consists in flowing the liquid to be evaporated in direct heat exchange contact with but countercurrent. to a gas or gas vapor mixture having a relatively lower temperature, the step. of increasing the ratio of the quantity of liquid to the quantity ofg'as or gas vapor mixture-in contact therewith when the temperatures thereof reach predetermined points intermediate the desired initial and final temperatures.

3. The process step of claim 2 wherein the variation in the ratio of the quantity of liquid to the quantity of gas orgas vapor mixture is ef fected by withdrawing a quantity of liquid from the quantity initially brought into contact with the gas or gas vapor mixture.

4. The process step of claim 2 wherein the variation in the ratio of the quantity of liquid to the quantity of gas or gas vapor mixture is effected by withdrawing aquhntity of gas or gas vapor mixture from the quantity initially brought into contact with the liquid. v

5. The process step of claim 2 wherein the variation in the ratio of the quantity of liquid to the quantity of gas or gas vapor mixture is effected bywithdrawing quantities of both liquid and/gas or gas vapor mixture from the quantity of each imtially brought into contact with the other.

6, The process of'evaporating liquids which til the temperature of said gas or gas vapor mixture is increased to a predetermined point, limiting the quantities of liquid and gas or gas vapor mixture in contact during the aforesaid portion of the process to a predetermined ratio, and then increasing the ratio of liquid to gas or gas vapor mixture and continuing the counterflow until the temperature of said gas or gas vapor mixture attains a still higher predeterminedpoint, whereby the process of evaporation can be carried out at a materially higher efliciency than if said ratio were maintained constant throughout the process.

7. A method of evaporating liquids which consists in heating by indirectcontact with a heating medium a certain quantity of liquid to be evaporated, then utilizing said same heating medium for indirectly heating another quantity of said liquid smaller'in quantity and of lower initial temperature than said first named quantity, and conducting a quantity of gas or gas vapor mixture of lower temperature than said liquids into direct heat exchange contact with but counter-current to said last named and first named quantities of indirectly heatedliquid successively to ,eiiect evaporation thereof.

8. The process of evaporating liquids which consists in flowing a certainquantity of the liquid to be evaporated at a relatively high initial temperature in direct heat exchange contact with but countercurrent to a gas or gasvapor mixture having a relatively low initial tempera ture until the temperatureof said gas or gas. vapoumixture is increased to a predetermined point, the temperature of said liquid being correspondingly lowered during the counterflow due to evaporation, and then bringing said gas or gas vapor mixture into direct heat exchangecontact with a; greater quantity of said liquid having an initial temperature higher than the initial temperature of said first named quantity and continuing the counterflow to efiect evaporation of said last namedquantity of liquid.

9. Theprocess of evaporating liquids which consists in flowing the liquid to be evaporated at a relatively high initial temperature in direct heat exchange contact with but countercurrent toacertainquantityof a gas or gas vapor mixture having a relatively low initial temperature until the temperature of said liquid is decreased to a predetermined point, the temperature of said gas or gas vapor mixture being correspondingly raised during the counterfiow due to evaporation, and then bringingsaidliquid into direct heat exchange contact with a greater quantity of said gas or gas vapor mixture having an initial temperature lower than the initial temperature of said first named quantity and continuing the counterflow to complete evaporation of the liquid.

10. The process of evaporating liquids whichv consists in flowing a certain quantity of the liquid to be evaporated at a relatively high initial temperature in direct heat exchange contact with but countercurrent to a gas or gas vapor mixture having a relatively low initial temperature until the temperature of said gas or gas 'vapor mixture is increased to a predetermined point, the temperature of said liquid being correspondingly lowered during the counterflow due to evaporation, then bringing said gas or gas vapor mixture into direct heat exchange contact with a.

greater quantity of said liquid having an initialj temperature higher than the initial temperature of said first named quantity and continuing the counterfiow to eifect evaporation of said last named quantity of liquid, heating the unevapoe rated portions of said quantities of liquid to their initial temperatures, and recirculating said heated portions through their respective evaporating cycles.

11. The process of evaporating liquids which consists in flowing a certain quantity of the liquid to be evaporated at a relatively high initial temperature in direct heat exchange contact with but countercurrent to a gas or gas vapor mixture having a relatively low initialtemperature until the temperature of said gas or gas vapor mixture 'is increased to a predetermined point, the temperature of said liquid being correspondingly'lowered during the counterflow due to evaporation, then bringing said gas or gas vapor mixture into, direct heat exchange contact with a greater quantity of said liquid having an initial temperature higher than the initial tem perature of said first named quantity and continuing the counterfiow' to effect evaporation of said last named quantity of liquid, heating the unevaporated portions of said quantities of liquid to their initial temperatures, and recirculating said-heated portions through their respective evaporating cycles, said heating stepjncluding the circulation of a quantity of heating medium of relatively high initial temperature in indirect contact with said unevaporated portions successively, the unevaporated portion of the last'named greater quantity of liquid being the first to be heated by said heatingmedium.

12. The processor evaporating liquids which 7 consists in flowing a certain quantity of the liquid to be evaporated at a relatively high initial temperature in direct heat exchange contact with but countercurrent to a gas or gas vapor mixture. having a relatively low initial temperature until the temperature of said gas or gas vapor mixture is increased to apredetermined point, the temperature of saidliquid being correspondingly lowered during the counterfiow due to evaporation, then bringing said gas or gas vapor mixture into direct heat exchange contact with a greater quantity of said liquid having an initial temperature higher than the initial temperature ofsaid first named quantity and continuing the counterflow to efiect evaporation of saidlast named quantity of liquid, heating independently of one another the unevaporated portions of said quantities of liquid to their initial temperatures by indirect contact with another gas vapor mixture; and recirculating said heated portions through their respective evaporating cycles.

13. A method of evaporating liquids comprising simultaneously circulating in two separate systems two different quantities of the liquid to, be evaporated, the liquid in each system first :being heated by indirect contact with a quantity of heating medium and then being flowed in direct heat exchange contact with but countercurrent to a quantity of gas or gas vapor mixture of a temperature lower than that of said liquid to effect evaporation of the latter, thelarger quantity of liquid being of the higher initial temperature, heating the different quantities of liquid in the two systems successively by the same heating medium by first utilizing the latter in the system containing the largerquantity of the liquid and then in the system containing the small er quantity, and evaporating said quantities of liquid successively by the same gas or gas vapor mixture but in the reverse order to that in which said quantities are heated.

14., In the method of evaporating liquids of claim 13, the step of transferring liquid from one system to the other between points at which substantially the same liquid temperatures prevail.

- 15. The method of evaporating liquids which consists in heating ,by indirect contact with a heating medium a certain quantity. of liquid to be evaporated, utilizing said same heating medium for indirectly heating another quantity of said liquidsmaller in quantity and of lower initial temperature than said first named quantity, conducting a quantity of relatively cold gas or gas vapor mixture into direct'heat exchange contact with but countercurrent to said last named quantity of indirectly heated liquid to effect evaporation of the latter by progressively decreasing the temperature of said liquid and increasing the temperature of said gas or gas vapor mixture,

and subsequently conductingsaid gas or gas vapor mixture at its increased temperatureinto direct heat exchange contact with but countercurrent to said first named quantity of indirectly heated liquid to efiect evaporation thereof.

16. The method of evaporating liquids which consists in heating by indirect contaot'with a heating medium a certain quantity of liquid to be evaporated, utilizing said same heating medium for indirectly heating another quantity of said liquid smaller in quantity and of lower initial temperature than said first named quantity, conducting a quantity of relatively cold gas or gas vapor mixture into direct heat exchange contact with but countercurrent to said last named quantity of indirectly heated liquid to eflect evaporation of the latter by progressively decreasing the temperature of said liquid and increasing the temperature of said gas or gas vapor mixture, subsequently conducting said gas or gas vapor mixture at its increased temperature into direct heat exchange contact with but countercurrent to said first named quantity of indirectly heated liquid to efiect evaporation thereof, and recirculating the unevaporated portions of said quantities of liquid through their respective heating and evaporation,

cycles.

17. Apparatus for the transmission of heat between a liquid and a gas or gas vapor mixture comprising a liquid receptacle having an inlet and an outlet, means for supplying arelatively cold liquid to the inlet of said receptacle, means for heating the contents of said receptacle, a pair of evaporating vessels each having a liquid inlet and outlet and an inlet and outlet for gas or gas vapor mixture, said evaporating vessels beingarranged in series with the liquid outlet of the first vessel connected with the liquiclinlet of the second and the gas outlet of the second connected with the gas inlet of the first, means for supplying relatively cold gas or gas vapor mixture to the gas inlet of said second evaporating vessel,

means for supplying heated liquid from the outv let of said liquid receptacle to the liquid. inlet of said first evaporating vessel, and means for varying the ratio of the quantity of liquid to thequantity of gas or gas vapor mixture in contact therewith as between said first and second evaporating vessels.

18. Apparatus for the transmission of heat between a liquid and a gas or gas vapor mixture comprising a liquid receptacle having an inlet and an outlet, means for supplying a relatively cold liquid to the inlet of said receptacle, means for heating the contents of said receptacle, a pair of evaporating vessels each having a liquid inlet and outlet and an inlet and outlet for gas or gas vapor mixture, said evaporating vessels being arranged in series with the liquid outlet of the first vessel connected with the liquid inlet of the second and the gas outlet of the second connected with the gas inlet of the first, means for supplying relatively cold gas or gas vapor mixture to the gas inlet of said second evaporating vessel, meansfor supplying heated liquid from the outlet of said liquid receptacle to the liquid inlet of said first evaporating vessel, means for varying the ratio of the quantity of liquid to the quantity of gas or gas vapor mixture in contact therewith as be tween said first and second evaporating vessels, and means for recirculating the liquid from the liquid outlet of said second evaporating vessel to the inlet of said liquid receptacle.

19. Apparatus for the transmission of heat.

between aliquid and a gas or gas vapor mixture comprising a liquid receptacle having an inlet andan outlet, means for supplying a relatively cold liquid to the inlet of said receptacle, means for heating the contents of said receptacle, a pair of evaporating vessels eachhaving a liquid inlet and outlet and an inlet and outlet for gas or gas vapor mixture, said evaporating vessels being arranged in series with the liquid outlet of the first vessel connected with the liquid inlet of the second and the gas outlet of the second connected wth the gas inlet of the first, means for supplying relativelycold gas or gas vapor mixture to the gas inlet of said second evaporating vessel, means for supplying heated liquid'from the outlet of said liquid receptacle to the liquid inlet of said first evaporating vessel, and means for reducing the quantity of the liquid entering the liquid inlet said second evaporating vessel below the-quantity leaving the liquid outlet of said first evapot a liquid anda gas or gas vapor mixtln'e comprising a liquid receptacle having an inlet and an outlet, means for supplying a relatively cold liquid to the inlet of said receptacle, means for heating the contents of said receptacle, a pair of evaporating vessels, each having a liquid inlet and outlet and an inlet and outlet for gas or gas vapor mixture, said evaporating vessels bein arranged in series with the liquid outlet oithe first vessel connected with the liquid inlet of the second and the ,gas outlet of the second connected with the gas inlet of the first, means for supplying relativelyc'old gas or gas vapor mixture to the gas inlet of said second evaporating vessel, means-for supplying heated liquid from the outlet of said liquidreceptacle to the liquid inlet of said first evaporating vessel, and means for reducing the quantity of the gas or gas vapor mixture entering the gas inlet ofsaid first evaporating vessel below the quantity leaving the gas outlet of said second evaporating vessel.

21. Apparatus for the transmission of heat between a liquid and a gas or gas vapor mixture comprising a pair of liquid receptacles each having an inlet and an outlet and being arranged in series with the outlet of the first receptacle connected with the inlet of the second, means for supplying a relatively cold liquid'to' the inlet of said first receptacle, means for heating the 'contents of said receptacles, a pair of. evaporating vessels each having a liquid inlet and outlet and an inlet and outlet for gas or gas vapor mixture,

said evaporating vesselsalso being arranged inseries with the liquid outlet oi the first vessel con nected with the liquid inlet at the second and the gas outlet of the second connected with the gas rat ng vessel. inlet of the.first, means for supplying relatively 0. Apparatus for the transmission of heat be- I cold gas or gas vapor mixture to the gas inlet of said second evaporating vessel, means for sun-.- plying heated liquid from the outlet of said second liquid receptacle to the liquid inlet of said first evaporating vessel, and means for cross connecting the liquid outlet of said first evaporating vessel and the inlet of said second liquid recep-y tacle.

22. Apparatus for the transmission of heat between a liquid and a gas or gas vapor mixture comprising a'pair of liquid receptacles each having an inlet and an outlet and being arranged in series with the outlet of the first receptacle connected with the inlet of the second, means for supplying a relatively cold liquid to the inlet oi said first receptacle, means for heating the contents-0t said receptacles, a pair of evaporating ves-' sels each' having a liquid inlet and outlet and an inlet and outlet for gas or gas vapor mixture, said evaporating vessels also being arranged in series with the liquid outlet of the first vessel connected with the liquid inlet of the second and the gas outletof the second connected with the gas inlet of the first, means for supplying relatively cold gas or gas vapor mixture to the gas inlet of said second evaporating vessel, means for supplying heated liquid from the outlet of said second liquid receptacle to the liquid inlet of said-first evaporating vessel, and means for drawing ofi a portion of the gas or gas vapor mixtureas it passes from the gas outlet of said second evaporating vessel to the gas inlet of saidfirst evaporating HANS ELIS ABRAHAM G6'I'I-I. 

